Utility of baseline assessment with FDG‐PET‐CT compared with CT Scanning in people with diffuse large B‐cell lymphoma (DLBCL)

Abstract

Introduction: We sought to establish whether a baseline FDG-PET-CT offers increased sensitivity compared to a baseline CT scan in people with diffuse large B-cell lymphoma (DLBCL) with Lugano stage II disease or above and to assess whether this might affect subsequent clinical decision making. Methods: We retrospectively reviewed all patients with newly diagnosed DLBCL over a 4-year period who had both an FDG-PET-CT and conventional CT scanning prior to any treatment. Discordance between the two studies was noted and the potential impact of this on clinical decision making was assessed, according to current British or international guidelines, specifically relating to the selection of primary treatment and the decision to offer therapy to prevent relapse in the central nervous system. Results: Between 2012 and 2016, there were 101 patients, M:F 59:42, aged 20 to 89 (median 54), who had a confirmed diagnosis of DLBCL (de novo DLBCL NOS 91; primary mediastinal B-cell lymphoma 4; previous low grade lymphoma with histological transformation to DLBCL 6) and had undergone both FDG-PET CT and a CT scan, which were available. In 39 cases (38%), there was discordance between the two imaging modalities. Anatomical sites detected by FDG-PET-CT but not by CT included: bone (13), spleen (5), adrenal gland (3), lymph nodes that were normal by size criteria but strongly tracer-avid (3), liver (2), and mediastinal soft tissue (2). Assessed by CT alone, 14 patients would have met formal criteria for the application of methotrexate via the parenteral or intrathecal route. With the information gleaned from FDG-PET-CT, a further 4 patients would have met criteria for this intervention. In addition, 3 patients who were assessed as having limited stage disease by CT had evidence of advanced-stage disease by FDG-PET CT scanning (splenic uptake, lymph nodes that were normal by size-criteria on CT that were clearly abnormal on FDG-PET-CT). This migration of their stage meant they would have received standard chemotherapy rather than being considered for combined modality therapy. FDG-PET-CT identified areas not related to lymphoma determined either on biopsy or clinical follow-up, thyroid disease (3), and nonspecific intestinal uptake for which no cause was found (2). Conclusions: In many patients, FDG-PET-CT identifies abnormalities not detected on CT scanning, even when the latter is reported by an expert lymphoma radiologist. Only a small number of these discordant findings result in a change in patient management, but these may have significant impact on individual patient outcomes. Therefore, we agree with the Lugano classification recommendation, published by Cheson et al, that FDG-PET CT should be applied at diagnosis in all patients with DLBCL. A biopsy or close clinical follow-up of atypical findings discovered on FDG-PET-CT is important, as findings other than lymphoma may produce a false-positive scan. Keywords: diffuse large B-cell lymphoma (DLBCL); positron emission tomography (PET)